Free d-amino acids in human plasma in relation to senescence and renal diseases

1. Minute but appreciable amounts of d-amino acids were detected in normal human plasma.

2. The content was significantly higher in an elderly population (age 76 ± 6 years, mean ± sd, n = 41) than in a younger group (age 42 ± 4 years, n = 26), i.e. 6.9 ± 4.8 nmol/ml (mean ± sd, range 0–18.8 nmol/ml) and 2.5 ± 1.8 nmol/ml (range 0–6.3 nmol/ml) for the elderly and the younger groups, respectively.

3. Elevation of plasma d-amino acid level was observed in a group of patients with renal disease (3.6–52.6 nmol/ml), in proportion to the serum level of creatinine (n = 50, r = 0.726, P < 0.001), β₂-microglobulin (n = 34, r = 0.551, P < 0.005), and to glomerular filtration rate (n = 39, r = 0.556, P < 0.001).